Im trying to repair my 1TB Seagate drive BSY error.

Have removed the PCB and connected to terminal port. Press ctrl+Z. I dont get the F3 T> prompt I was expecting only >


if I type in ? I get

Boot Cmds:
DS
AP <addr>
WT <data>
RD
GO
TE
BR <divisor>
BT
?
RET

if I type in GO the drive responds


TetonST Boot Rom 2.0
Copyright Seagate 2006


Any ideas ?

I think you may have damaged your ROM if this is the terminal output recieved on power on.

there is much information available about this fault, it has been discussed in much detail in many topics. I suggest you get professional assistance, or spend a long time reading more on the problem, especially on the detremental effects of messing with the firmware without a good understanding of exactly what it is you are doing.

For me, ROM is gone or something weird on the PCB. It seems the MCU resident boot loader.

Bad result of do it yourself without proper initial diagnose.
Maybe not irrepairable (don't know what exactly you have done even if I can imagine), but now it will cost you a lot. Can't tell you more, sorry.